This lens is excellent in image quality and can be compared with legendary Takumars like SMC 85 1.8,Super Takumar 50 1.4 and Super Multi Coated Takumar 135 f2.5 (6 Elements) Version.Not a common focal length to use and probably that is the only reason it is not so famous or widely used.You find very few images on the internet when searched for this lens .Hopefully I'll add more images hereafter one my flickr page(link below).

Found this lovely lens for a mere $40.00
It is durable, has a nice weight, great bokeh, and works like magic for macro shots.

Focus is nice and smooth. It's rare to stumble upon a telephoto lens that is f/2.8, so I'd get this one if I was trying to save money. The 120mm is strange choice for a full frame sensor, it's close up, but not enough to get extremely far shots.

Soft enough for woman portraiture at f/2.8 (but it might lack of sharpness for very detailed objects), sharp enough for men portraiture when stopped (f/4 is enough). Bokeh is rather smooth and S-M-C coatings are efficient.
As the 105/2.8 and 135's are often cheaper, I would recommend it only to some one who really need it (for its caracteristics) or a collector.
Some portraits with it : http://kajiwara.weebly.com/takumar-12028.html

I have owned this lens for about a year now, and I have to tell you, it's probably my favorite Takumar. I have an M42 135mm 2.5 Super Takumar as well, and the 120 2.8 makes the 135 look like garbage on my K200D (Perhaps I have a bad copy of the 135). The 120 2.8 is a lot smaller and lighter than the 135 2.5, and the focal distance is not that much different, so I may be getting rid of the later.

This lens is a decent length for outdoor portrait work, and your subject is sharp even at 2.8. The bokeh from this lens is also very nice.

As the previous reviewer stated, this lens is not too common. If you are lucky enough to get your hands on one, I am sure that you'll like it.

Another classic long S-M-C Takumar lens. The all metal build quality is very nice, and the lens feels like it is fresh from the factory mounted on my K20D.

This lens is quite fast for its focal length at 2.8, and the photos is shoots wide open are not overly soft at all. By f4 or 5.6 the lens is very sharp and extremely good looking. I think my favorite bit about all the S-M-C Taks is the color rendering. The colors are just beautiful, bokeh is buttery soft and often yields an amazingly 3-d quality to foreground subjects.

I would say this lens would be very suited for longer distance street photography, maybe some portrait photography, and close subject stuff like flowers and butterflies.

I will say the only detraction for this lens is the focal length on a DSLR.... just a bit too long for portrait work and too short for wildlife work (except maybe the zoo).

This lens is rare, but if you can find one it is a very worthy addition to your kit as a long, fast prime! Love that Takumar look!!